The present invention relates to engine analyzers used for testing internal combustion engines. In particular, the invention relates to displaying waveforms generated by an internal combustion engine.
One common type of engine analyzer used for testing an internal combustion engine employs a cathode ray tube having a display screen on which analog waveforms are displayed which are associated with operation of the engine. In a typical apparatus of this type, a substantial horizontal trace is produced on the screen of the cathode ray tube by applying a sawtooth ramp voltage between the horizontal deflection plates of the tube while the analog signal being measured is applied to the vertical deflection plates of the tube. The typical analog signals which are applied to the vertical plates of the cathode ray tube are the primary voltage which exists across the primary winding of the ignition coil, and a signal representative of the secondary voltage of the ignition coil. These voltages are affected by the condition of various elements of the ignition system of the engine, such as the spark plugs.
In the case of a multicylinder internal combustion engine, the primary and secondary voltage waveforms have typically been displayed on the cathode ray tube in one of two ways. In one case, the waveform being displayed represents a complete cycle of the engine, in which the conditions associated with the various cylinders are displayed sequentially in a predetermined pattern. This type of display has commonly been referred to as a "parade" pattern or display.
In the other common method of displaying waveforms, there are a plurality of horizontal traces, one above the other, with each trace being associated with the operation of one of the cylinders of the engine. The number of horizontal traces usually corresponds to the number of cylinders on the engine. This method of displaying waveforms has been referred to in the industry as a "raster" display. Analog displays are desirable because they are able to display high frequency waveforms in real-time.
With the advent of low cost microelectronic devices, and in particular microprocessors, digital electronic systems have found increasing use in a wide variety of applications. Digital electronic systems have many significant advantages over analog systems, including increased ability to analyze and store data, higher accuracy, greater flexibility in design and application, and the ability to interface with computers having larger and more sophisticated data processing and storage capabilities. U.S. Pat. No. 4,399,407 issued to Kling et al. on Aug. 16, 1983, entitled ENGINE ANALYZER WITH CONSTANT WIDTH DIGITAL WAVEFORM DISPLAY and U.S. Pat. No. 4,476,531 issued to Marino et al. on Oct. 9, 1984, entitled ENGINE ANALYZER WITH DIGITAL WAVEFORM DISPLAY are examples of an engine analyzer using a digital waveform display, and are incorporated herein by reference.
Typically, digital waveform displays in engine analyzer systems have been unable to display "live" engine waveforms. This is due to the slow speed of the waveform conversion and display circuitry and the high frequency of some engine waveforms. For example, an engine analyzer typically takes an entire set of samples over the desired portion of an engine waveform and stores the samples in memory. After the waveform is sampled, converted to a digital format and stored, the engine analyzer retrieves the samples from memory, converts them into a display format and displays the samples on a waveform display.
There is a continuing need for improved engine waveform displays in internal combustion engine analyzers.